A ZF transfer case should be power up, FWD disengaged. Power down, FWD engaged. If you have power on the solenoid, you likely have a weak solenoid. They still spark a bit, and will click enough to screw with your head and make you think it works. A weak solenoid will work to some degree. It is more noticeable on the road. If you disengage the FWD at road speed, you should notice the difference in noise. A weak solenoid will then gradually allow oil to seep through and reenergise the FWD. Noise/whine will gradually grow louder. Let's hope for a bad fuse. Solenoids are several hundred bucks, and odds are, the solenoid is bad. HTH.